No one knows how long it will take specifically, but as humans are emotional beings things tend to escalate fast once things start to go wrong. This has been seen many times in history where civilizations has gone from nothing, to great success or from great power to sudden total destruction.
The speed of the progress usually depend on the speed of the good to see the truth and live it, and the bad to deny the truth and forcefully reject it.
Three of the key areas where these things escalate fast is in
1. Morality, which is needed for law, order, unity, safety, justice, motivation to work and ...